The invention relates generally to fiber optic communication technologies, and more specifically to a system and method for tuning optical fiber Bragg grating by a mechanically induced strain along the fiber.
It is well known that the wavelength center of fiber Bragg gratings can be shifted by either temperature or strain variations, or both. These tuning properties have been widely used in telecommunications.
Chromatic dispersion in a single mode optical fiber is an important problem to solve when such optical fibers are used for telecommunication. This phenomenon induces an undesirable broadening in data pulses, which appears because there is a time delay between different wavelength components. In order to eliminate this kind of dispersion, the negative dispersion exhibited by linearly and non-linearly optical fiber Bragg gratings has been widely used.
Because chromatic dispersion depends on the characteristics of the fiber in a telecommunications system, a grating with an adjustable chirp is more convenient for its compensation.
Tunable devices stretching a chirped fiber grating to compensate for the chromatic dispersion produced by single mode fibers in optical pulses are prior art. All of them, however, apply strain along the fiber grating in a linear fashion.
For those applications where long fiber gratings are needed, the use of long stretcher mechanisms increases the dimensions of dispersion compensations systems. On the other hand, mechanical vibrations alter the spectral characteristics of a fiber grating, either if is suspended or bonded, when using long linear stretcher mechanisms. This affects the performance of the tunable dispersion compensation devices.
For example, in U.S. Pat. No. 5,999,671, a device is shown that is longitudinally stretched to change the central wave length of the Bragg grating, and accomplishing the same function is shown in U.S. Pat. No. 6,055,348 which uses magnetostrictive devices, the disclosures of which are hereby incorporated herein be reference. As discussed above, these patents, while perhaps accomplishing the desired end result, do so at the cost of size and complexity. Another disadvantage is the lack of uniformity along the longitudinal axis of the servo strained element.
A different type of arrangement for changing the Bragg filter center frequency is shown in U.S. Pat. No. 5,007,705 where a cylindrical piezoelectric device is shown wrapped with the fiber around its outer circumference, the disclosure of which is hereby incorporated herein by reference. Upon the application of an energy source, the piezoelectric element changes its diameter thereby changing its circumference so as to adding more or less strain onto the transmission cable. This changes the Bragg filter center wavelength. This patent is also hereby incorporated by reference herein.
The present invention is directed to a system and method for tuning an optical fiber Bragg grating by using a circular mechanism which uniformly stretches the fiber along its length while at the same time preserving the minimal size for stretching. This method may also provide a smaller package footprint for chromatic dispersion compensation.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.